Sound reproduction



4 Sheets-Sheet 2 H. l. REISKIND SOUND REPRODUCTION Filed April 30, 1941 Oct. 20, 1942.

6a 65 FIG. 4. I

Ol/TPl/I' CONTROL VOLT/7GB Jnventor Hillel l. Heialiin I/VPl/T CONTROL VOL 'IWGL' Oct. 20, 1942. H; REISKIND ,2

SOUND REPRODUCTION Filed April 30, 1941 4 Sheets-Sheet 3 OUTPUT CONTROL var. TflG-E Ffa. 6.

19 .B C CONTROL TfiflC/f RELATIVE OUTPUT ow'Pu'r y I F26. 7.

A B C D CONTROL TFHCK FELflT/VE OUTPUT;

Zmnentor Hillel l-Heisliind (Ittbmeg Oct. 20, 1942. H. l. REISKIND 2,299,410

SOUND REPRODUCTION Filed April 30, 1941 4 Sheets-Sheet 4 mil" 104 +250 conl'riiol; {IQ FM). 3 g z sou/v.2) 101 TF/ICK 102 i 106 k J05 Enventor Hillel I. Heisliind' 16 18 '60 '20 l az/v'rm? 10 V 14 I awa /raps W 'l Z1 I J sol/mp TfiWC/f I v the speakers.

Patented Oct. 20, 1942 SOUND REPRODUCTION Hillel I. Rteiskinilndianapolis, Ind., assignorto Radio Corporation of America, a corporation of Delaware Application April 30, 1941, Serial No. 391,161

9 Claims.

This invention pertains to the reproduction of sound, and, more particularly, to the photoelectric reproduction of sound from film type sound records, In a sound reproduction system to which this invention is applicable, a plurality of loudspeakers or sets of loudspeakers are used, and the reproduction of sound through the several speakers is controlled as to both volume and clal control track recorded on the film and reproduced concurrently with the sound track.

This application. is in general an improvement on the apparatus described and claimed placement in a predetermined inanner by a spein M. C. Batsels application Serial No. 302,197,'

improved apparatus for controlling the placement of sound reproduction,

Another object of the invention is to provide an improved apparatus for controlling the volume of sound reproduction.

Another object of the invention is to provide an improved film sound reproducer.

Another object of the invention is to provide means for selectively or' collectively controlling a plurality of sound reproducer Another object of the invention isto provid improved variable gain amplifiers for controlling the volume of sound reproduction.

Other and incidental objects of the invention will be apparent to those skilled inthe art and from a reading of the following specification and plication SerialNo. 181,634, filed December 24,

1937, wherein a control record is placed in the sprocket hole area of the sound record or motion picture film, and the sprocket hole frequency is used as a carrier frequency which is modulated in amplitude in accordance with the control effect desired. The sprocket hole frequency may be modulated as to frequency, if desired, in accordance with C. M. Burrills application Serial No. 181,635, filed December 24, 1937. The invention is not limited, however, to the use of these specific types of control tracks, as the control track might be located in the margin of the film beyond the sprocket hole area, as described for example in British Patent 309,208 to Wilson. Alternatively, a subaudible or superaudible control frequency might be superposed on the soundrecord as described and claimed in Ringel Patent 2,029,389, issued February 4, 1936.

The present invention involves a novel method of and apparatus for controlling the speakers and amplifiers by means of the control track or control frequency, and involves the placing into operation or removing from operation of additional speakers and amplifiers either with or without change of volume at the time the additional elements go into or out of operation and the subsequent control of the volume of reproduction from either all One object of the invention is to provide an or a selected portion. of-

an inspection of the accompanying drawings in which:

Figure 1 is a block diagram of 'the preferre form of the invention,

Figure 2 shows one desired set of characteris tic curves,

Figure 3 is a schematic diagram of the control amplifier indicated in Fig. ,1,

Figure 4 is a schematic diagram of the first variable gain amplifier shown in Fig. 1,

Figure 5 is a schematic diagram of the second variable gain amplifier shown in Fig. 1,

Figure 6 shows the desirable characteristic for the apparatus in order to provide control of gain on'the center speaker without the side speakers turned on,

Figure 7 illustrates the gain characteristics of the system shown in Fig. 8,

Figure 8 is a block diagram of a modified form ofthe invention using three variable gain amplifiers, and

. light l0 and a photocell It. This scanning system is, of course, constructed in accordance with usual commercial practice and may include an optical system, a slit and other such elements as might be necessary or advisable to insure proper reproduction of the sound, there being many varieties of such'system shown in the patented art. The control track at I 3 is likewise reproduced by means of an appropriate light such as indicated at II and a photocell 15. The l output from the photocell I4 is passed through a voltage amplifier I6 which may be made in accordance with usual commercial practice and the output from the voltage amplifier is fed to the first variable gain amplifier I8 schematically ilthe side speakers .24 with their poweramplifier 22 will increase the overall sound level by approximately 3 db. If these speakers are of the same power as the screen speakers, this effect may be avoided by decreasing the gain of the first variable gain amplifier I8, as indicated in the dotted line 34, as the side speakers are gradually brought intooperation. The overall output thenremains constant, as the side speakers are brought into operation and, after they are completely operating, the gain on the first am-- plifier I8 may be increased, as indicated in the. dotted line 35, until the full output of the ap- I paratus is attained.

two of which are applied to the variable gain amplifier I8 and the third of which is applied to a second variable gain amplifier I9. The variable gain amplifier I9 takes its input from a. circuit between the variable gain amplifier I8 and the power amplifier 28 and the output from the variable gain amplifier I9 is fed through the power amplifier 22 to the speakers 24 which are located, respectively, at the sides of the screen speakers 2] and are preferably symmetrically. lo-

I cated. in respect thereto so as to give the effect of the reproduction of sound from an extended The solid lines in Fig. 2 represent one desired set of gain characteristics of the variable gain amplifiers plotted against the control track out,- put. The point Aof the control track output represents the minimum modulation from the control track, which is bucked out in the control amplifier so it has no effect on the system. This minimum modulation unavoidably occurs on any photographic type of control track or even on a mechanically reproduced control track due to the physical characteristics of the record material. For example, in the sprocket hole type of control track the film between the sprocket holes is not completely transparent and there is there- The control amplifier for accomplishing this result is shown in detail in Fig. 3. The control track output from the photocell I5 is fed to the vacuum tube 36. typ and is operated as a logarithmic amplifier. As will be apparent from an inspection of the diagramfthe positive terminal plate supply voltage is grounded and all voltages in the circuit are negative withrespect to ground in order to secure negative bias on the grids of the variable gain amplifiers. The tube 36 is provided with the usual suppressor grid and screen grid which are connected in the customary manner, but the control grid nearest the cathode is rendered positive in relation to the cathode. It will be apparent from the circuit diagram that the photocell I5 is connected to a source of potential some 90 volts more positive than the cathode, and any current passing through the photocell I5 will, therefore, appear in the tube 36 in the form of grid current. Under this condition, the tube acts as a logarithmic amplifier, and the level of the A. C. signal produced is rendered independent of the brightness of theexciter lamp, being determined substantially entirely by the ratio between the maximum and minimum brightness,

rather than the difference between maximum the rectifiers 38 and 40. Each of these rectifiers reaches a maximum value. As the control track output increases from its minimum value A,

the gain of the second ariable gain ampli- 'fier I9 may be increased as indicated in the attained.

This arrangement has what, in some instances,

may be a disadvantage in that the addition of is a full wave rectifier connected as shown in a conventional doubler circuit, and differs from the usual practice only on the provision of the potentiometers 45 and 46 which provide a bucking bias on each of theserectifiers to eliminate the minimum output from the control track described above. The output from the rectifier 38 is supplied through the circuit shown to the amplifier 39. The potentiometer 41 at the output circuit of the rectifier 38 determines the average amplitude of the control potential applied to the .tube 39, while the resistor 48, which may have 'a This tube is of the pentode the cathode and, therefore, no grid current is drawn. The plate current of the tube 39 is applied across the potentiometer 59 from which the control voltage of the circuit marked A in Figs. 1 and 4 is taken. may be provided with further filtering means consisting of the resistor 53 of one megohm value and an appropriate condenser 56, which, like the condenser 5|, may 'havea value of microfarad.

The first variable gain amplifier is shown in Fig. 4. In this amplifier the audio input is fed through the transformer 60 to the tube 6|. The tube 6| is a standard type of exponential tube such, for example, as the type 6K7 the gain of which varies with the grid bias. The plate supply of this tube is fed through the inductance 6! while the audio frequency output is taken out through the transformer 65 connected in series taken across the resistor 59 or capacitor 56 of Fig. 3, as described before, while the control voltage C is the voltage which appears across the capacitor 5| in Fig. 3. With a control voltage B suificient to cut off the second variable gain amplifier indicated at l9 in Figure l the control voltage 015 so adjusted as to put the proper load on the plate circuit of the tube 6|. When the control track operates to drive the control volt age B to zero thereby turning on the power amplifier 2 2 and the loudspeakers, the control voltage C is also driven to zero thereby putting an additional load on the plate circuit of the tube 6| which load is determined by the plate-to-cathode resistance of the tube 63 and the value of the resistor 64. This reduction of the control voltage C reduces the gain of the first variable gain arn-' plifier 18 of Fig. 1 and if the constants of" the circuit are properly adjusted the operation of the device will follow the curve 34, 35 of Fig. 2 giving no observable change in level in the auditorium when the additional speakers are turned on. The control voltage A is varied in the manner before described and increases the gain of the tube 6| after the side speakers are switched on up to the point of maximum output as indicated in Fig. 2.

The' connections to the second variable gain I amplifier H! which is used to turn on the side speakers are shown in Fig. 5. In this amplifier,

the audio input from the first variable gain am? plifier is supplied through the transformer 10 to the tube II, which, like the tube Bl of the amplifier of Fig. 4, may be a type 6K7. The audio output from the tube 1| is fed through the transformer 14 to the power amplifier 22 of the side speakers, plate voltage being supplied to the tube 1 Lthrough the resistor l3. An appropriate voltage divider 12 provides the normal grid bias and screen potential for the tube. This amplifier is, as shown in the drawings, supplied with the control voltage developed across the capacitor 58 in the lower portion of the amplifier shown in'Fig. 3, and this voltage is suflicient to bias the tube ll completely to cut-off, being decreased as above described when it is desired to turn on the side speakers.

If desired, this output circuit curves of Fig. 6.

While the above described scheme of first turn ing on the side speakers and then volume-controlling the entire system is the one which is at present preferred, other modes of operation may be used. For example, it may be desired, under some circumstances, to control the volume of the system with only the center speaker operating and only turning on the side speakers after maximum gain has been reached on the first variable gain amplifier. Such an arrangement would have the advantage of providing a wider volume range for solo or dialogue parts, for example,

which must be reproduced on a single speaker, .while the multiple speaker system would be available for orchestra reproduction.

In order to secure this type of operation of the amplifiers, the controls of the amplifiers would have to be set in accordance with the curves ,shown in Fig. 6. In this instance, the potenset to buck out the control voltage represented by the point B on the curves of Fig. 6 and above tr 5 volt-age'the signal from the side speakers would be gradually turned on. Thepotentiometer 48 is set to drive the tube 4| to cut-off at the control voltage C of the curves of Fig. 6, which is the maximum control voltage developed by the control track. 7 7

If itis desired to secure a combination of the foregoin effects, this may be done by soconnecting the apparatus that'the gain for the center speaker may be controlled,the side speakers may then be turned on, and the volume of the entire apparatus may thereafter be further increased.

One arrangement of apparatus for accomplishing this result is shown in Fig. 8, the operation of this apparatus being controlled in accordance with the curves of Fig. 7. The apparatus of Fig. 8 difiers from that of Fig. 1 in the interposition of the additional variable gain amplifier 80 between the-amplifier I8 and the power amplifier 20, the control amplifier ll being provided with an additional rectifier tube corresponding to the tube 40 and connected in the same manner. With this arrangement, with the control signal between zero and the, point marked A in the curves of Fig.7, the reproducer gain is unaffected and the side speakers are off. As the control signal increases from its minimum value at A to some predetermined value indicated at B, the .reproducer gain is increased as shown in the upper curve of Fig. 7, while the side speakers remain off. As the control track signal increases from B to C,.

the reproducer gain remains at its intermediate value and the side speakers are turned on by the second variable gain amplifier IS in the same manner as described abovein connection with '-Fig. 2. Asthe control signal increases from the justment of the apparatus in this arrangement is accomplished in the same manner as in the preceding arrangement.

The result accomplished by the apparatus of The potentiometer 46 would be Fig. 8 may also be accomplished without the addition of a third amplifier by the use of the circuit shown in Fig. 9. In this circuit, the control signal is fed to the transformer 82 provided with three secondary windings to the rectifiers 83,84 and 85. These rectifiers are provided with batteries 80, 86 and 87 connected in opposition to the control signal and having values hereinafter described. The output of the rectifier circuits is applied across the potentiometers 88, 89 and 90, and an appropriate proportion'of the output voltage is filtered by the resistors 9I, 92 and 93 I and the capacitors 9|, 92', 93' and applied to the amplifiers 94, 95 and 96. The amplifiers 94, 95 and 98 may be triodes, as shown. or they may be pentodes with their screens fed from a constant voltage source, so that moderate changes in plate voltage will not produce serious changes in plate current. The plate current for the tubes 94 and 95 is taken through the common resistor 91 which also serves as a potentiometer and is fed to these tubes through the series resistors 99 and I00, respectively. It will be apparent that any decrease in the plate current of' either the tube 90 or 95, or both, will produce a corresponding decrease in the drop across the potentiometer 91 and .will correspondingly afiect the bias on the control grid of the amplifier tube I02. The tube I02 corresponds with the first variable gain amplifier in the preceding forms of the invention and is fed with the sound currentthrough the trans former II'.

The tube I02 is supplied with' appropriate screen and cathode potentials through the voltage divider I04 and is supplied with plate current through the resistor I03. The audio output of the tubeI02 is supplied through the transformer I05 to the center speaker IOBand throughthe transformer I0Ito the second variable gain amplifier which, in this form of the invention, is the tube I08. The tube I00 is supplied with cathode and screen potentials-by the voltage divider H0 and with plate current through the resistor I09.

The audio output of the' tube I08 is fed to the side speakers H3 through the transformer I I2.

The gain of the tube I08 is controlled by the amplifier 96, the plate current of which, applied to the tube I02-through the potentiometer 91.

' The voltage at 86 is set to buck out the control voltage of the value indicated at C in Fig. 7, and the potentiometer 88 is set so that the control tube 90 is cut-off at the control voltage D of Fig. 7, which is the maximum voltage produced by the control track. a

With no control signal, the current through the resistor 90,-which is the sum of the plate currents of the tubes 94 and 95, biases the tube I02 to its minimum gain. As the tube 95 is out off as the control voltage increases from the value A to the value B in Fig. 7, the drop across the resistor I5 isreduced, thus raising the gain of the tube I02 to an intermediate value determined by the resistor I00. An increase in the control signal from the value B to the value C of Figure '7 has no effect on the tube I02, although this increase affects the tube I08 to turn on the side speakers. As the control signal further increases from the value C to the value D, the tube 99 is cut off, correspondingly decreasing the current through the resistor 91 and increasing the gain of tube I02 from its intermediate to its maximum value. This latter increase being adjusted -by the resistor 99. I

I claim as my invention: V

1. In combination, a sound current pickup, a sound reproduction channel, a control current pickup, a control amplifier actuated by said control current and a plurality of variable gain amplifiers in the sound reproduction channel controlled by-difierent ranges of output level of the said control amplifier.

2. In combination, a sound-current pickup, a sound reproduction channeL, a control current pickup, a control amplifier actuated by said control current and a plurality of'independent variable gain amplifiers in the sound reproduction channel independently controlled by different ranges of output level of the said control ampli- 3. In combination, a sound current pickup, a plurality of sound reproduction channels, a con-. trol current pickup, a controlamplifier actuated by said control current and a plurality of-independent control means in the sound reproduction channels independently controlled by different ranges of output level of the said control amplifier.

4. In combination, a sound current pickup, a plurality of sound reproduction channels, a control current pickup, a control amplifier actuated by said'controlcurrent and a plurality of independent variable gain amplifiers in the sound reproduction channels independently controlled by different ranges of output level of the said control amplifier.

5. In combination, a sound current pickup, a plurality of sound reproduction channels, a control current pickup, a control amplifier actuated trol voltages up to the valu indicated at B in.

Fig. '7, and the potentiometer 90 is set to drive the control tube 96 to cut-ofi at the control voltage indicated at C in Fig. I. The side speakers are thus turned on as the control voltage increases from the value B to the value C in Fig. 7.

The voltage at 86' which, as indicated above,

may be supplied by a batterylor some other suitable power supply across a potentiometer, is set to buck out the control voltage A, which is the minimum signal from the control track and the potentiometer 89 is set to drive the control tube 01 voltage B; thereby 95 to cut-off at .the cen correspondingly increasing the potential supplied by said control current and a plurality of control means in the sound reproduction channels controlled by the said control amplifier, at least one of said control means being a variable gain amplifier controlling the input to all of said channels.

6. In combination, a sound current pickup, a plurality of sound reproduction channels, a control current pickup, a control amplifier actuated by said control current and a piurality of inde= pendent variable gain amplifiers in the sound re .;;-.roduction clhannels controlied by the said con trol amplifier, one of said variaielz gain amplifiers -gthe input to allot s channels.

control current pickup, a main sound reproducer,

auxiliary sound reproducers, a variable gain amplifier controlling the sound volume, and an additional variable gain amplifier controlling the operationof the said auxiliary reproducers, both of said variable gain amplifiers being controlled from said control current pickup, and means connected to each of said variable gain amplifiers restricting its operation to a predetermined range of output amplitude of said control cur rent pickup.

9. In combination, a sound current pickup, a control current pickup, a main sound reproducer, auxiliary sound reproducers, a variable gain amplifier controlling ,the sound volume from the main sound reproducer, and an additional variable gain amplifier independently controlling the sound volume from said auxiliary reproducers, both of said variable gain amplifiers being controlled from said control pickup, and means connected to each of said variable gain amplifiers restricting its operation to a predetermined range of output amplitude of said control current pickup.

HILLEL I. REISKIND. 

